ex20.py

 1 # -*- coding: utf-8 -*-
 2 from sys import argv
 3
 4 script, input_file = argv
 5
 6 def print_all(f):
 7     print (f.read())
 8
 9 def rewind(f):
10     f.seek(0)
11 #seek那个函数不返回值，你print淡然显示为None了，file.seek(0)是重新定位在文件的第0位及开始位置
12 #file.seek(3) 定位到第3个
13
14 def print_a_line(line_count, f):
15     print (line_count, f.readline())  #如果readline 中加入数值，看看什么含义？
16
17 current_file = open(input_file)
18
19 print ("Frist let‘s print the whole file:\n")
20
21 print_all(current_file)
22
23 print ("Now let‘s rewind, kind of like a tape.")
24
25 rewind(current_file)
26
27 print("let‘s print three lines:")
28
29 current_line = 1
30 print_a_line(current_line,current_file),   #X += Y 和X = X + Y 意思相同
31
32 current_file.seek(20)   #注意到这个作用，它是将readline()中的读取后光标的位置重新定位到seek()中字符的位置
33
34 current_line = current_line + 1
35 print_a_line(current_line,current_file),
36
37 current_line = current_line + 1
38 print_a_line(current_line, current_file)